pgsql: Fix mapping of PostgreSQL encodings to Python encodings.

Fix mapping of PostgreSQL encodings to Python encodings.

Windows encodings, "win1252" and so forth, are named differently in Python,
like "cp1252". Also, if the PyUnicode_AsEncodedString() function call fails
for some reason, use a plain ereport(), not a PLy_elog(), to report that
error. That avoids recursion and crash, if PLy_elog() tries to call
PLyUnicode_Bytes() again.

This fixes bug reported by Asif Naeem. Backpatch down to 9.0, before that
plpython didn't even try these conversions.

Jan Urbański, with minor comment improvements by me.

Branch
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REL9_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/773288016d00bd72e8e2bcb5b1eec67abb2d9e00

Modified Files
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src/pl/plpython/plpy_util.c | 69 ++++++++++++++++++++++++++++++++++++++----
1 files changed, 62 insertions(+), 7 deletions(-)